Vibrator circuit



Feb. 3, 1948. 'r. N. ROSSER vmm'rbn cmcun Filed Dec. 15, 1943 RETARDED RELAY INVENTOR.

RETARDED DIFFERENT/AL RELAY THEOQORE N. nossgn Patented Feb. 3, 1948 UNITED STATES PATENT OFFICE vmaa'roa omourr Theodore N. Rossenlndianapolis, 1nd,, assignor to P. R. Mallory 8a 00., Inc., Indianapolis, Ind., a corporation of Delaware Application December 15,1943, Serial No. 514,315

' '1 Claims. (61.1'11-9'1) greatly exceed the wear on the contacts caused by many hours of steady-state normal operation.

When the starting switch is closed to connect the battery or other low voltage direct current source to the vibrator and to'the primary winding of the step-up transformer, the vibrator ma net of relatively high resistance is first energized and will initiate the swing of the vibrator reed. As soon as the reed has swung far enough to close one pair of the vibrator. contacts, a low re-' sistance circuit is established through half of former having a primary winding with a center tap and a, vibratory contact system causing current taken from the low voltage source alter nately to flow through the two halves of such winding. In most cases provision is made for rectification of the high voltage alternating current output, this being accomplished in the simplest case by means of synchronous rectifying contacts arranged on the vibrator or by means of a suitable rectifier tube.

Although vibrator systems have been already developed to a high degree of reliability, serious difliculties have been experienced in providing vibrators having a long useful life. It has been found that the weakest elements of conventional vibrator systems are the contacts controlling the primary circuit. Since the vibrator is required to interrupt a circuit having a high inductance, the power contacts are subject to the possibility of severe destructive arcing. This danger is accentuated by the recent tendency of employing considerably higher battery voltages, such as 12 to 15 and 24 to 30 volts, this being the case particularly with aircraft installations. Prior remedies included the provision of heavy-duty contact discs made of special alloys, judicious design of the step-up transformer and also the insertion of suitable builer condensers bridged across the transformer windings. None of these remedies,

1 however, has provided a completely satisfactory solution of the outstanding problem.

Itrhas now been discovered that the relatively short useful life of vibrator contacts was not due to steady state arcing conditions, which could be readily kept at a relatively low level, but to unusual arcing conditions encountered during the first few starting cycles of the vibrator, particularly during its first half cycle of operation. Exhaustive experiments carried out in this direction have demonstrated that the tranthe transformer winding, and current from the battery immediately begins to build up in this cir-, cuit. Since the resistance of this circuit isquite low, the rate of current increase is controlled principally by the counter EMF developed in the half transformer winding by the-change of magnetic flux in the core. During steadyrstate operation of the vibrator the magnetic flux will be reversed in direction during each vibrator half cycle. It will be apparent, therefore, that if the pulse.

regarding saturation conditions of'the iron core,

sient arcing conditions existing for a small fraction of a second during the starting of the vibrator will cause damage that may equal or even system is designed so that the transformer will have a maximum flux of Fm at the end of each half cycle period, the total change in flux during a half cycle will be from -Fm to 44%, or 2Fm.

It has been found, however, that altogether different conditions of flux will prevail during the starting cycles of the vibrator. Thus, during the starting half cycle, the flux at the start will be determined by the residual magnetism in the iron core of the transformer. In many cases this may amount to as much as .8Fm and may be in the same direction as the initial magnetizing im- Itwill be evident therefore, that, disthe current which builds up through the transformer winding during the first half cycle will create a flux which may be additive to the residual magnetism of the core to produce a total flux of 2.81% in the transformer by the end of the first half cycle when the vibrator contacts open.

In practical vibrator power units. saturation of the transformer core-may occur before this flux density is reached, in which case the current through the primary winding will increase to excessively high values. Therefore, at the end of the first half cycle of operation, when the first pair of vibrator contacts opens, a much higher current will be flowing in the primary winding than is attained during steady operaton, and the flux will also be much greater than Ffm. Of course. this condition of excessive current and excessive flux density imposes severe arcing conditions on the vibrator contacts as they open, and these unusual and transient arcing conditions cannot be fully controlled by the bufier condensers normally connected in the circuit, without employing such large values as to involve damaging results during the steady-state operation, as well as uneconomical size and cost.

To reduce the severe arcing conditions during starting, it has already been attempted to incorporate certain changes in the design of the stepup transformer. This, however, at best provided a rather poor compromise since the efiiciency of the transformer during steady operation was also greatly reduced, or the physical size greatly increased. Such expedients have not been completely successful even with relatively low operating voltages and the problem is greatly aggravated where batteries of a voltage higher than six volts are used, such as in aircraft electrical systems where voltages of 14 to 28 volts are quite common. This results from the greater ease of ionization of the air between the contacts at the higher battery voltages, thus facilitating forming of destructive arcs.

It is an object of the present invention to provide a simple and completely satisfactory solution of the outstanding problem.

It is another object of the present invention to provide a novel and improved vibrator system which is substantially free from the unusual and severe arcing conditions unavoidable in conventional vibrator systems, and which consequently makes it possible to considerably increase the useful life of the vibrator without decreasing the overall electrical efficiency of the system.

It is a further object of the present invention to provide a novel and improved vibrator circuit organization involving current limiting means restricting the maximum current during the initial cycles of vibrator operation and delayed action means for disabling such limiting means after the steady or normal operation has been reached.

The invention also contemplates the incorporation of electromagnetically retarded switching means into a vibrator circuit which automatically maintains preferred operating conditions both during the starting and the steady operation of the vibrator system and thereby permits combining extremely long useful life of the vibrator system with great electrical efficiency.

Other and further objects and advantages of the invention will be apparent from the following description taken in conjunction with the accompanying drawing, in which Fig. 1 is a circuit diagram of a vibrator system embodying the principles of the present invention and including a retarded relay with a serially connected winding;

Fig. 2 is a similar circuit diagram of a modified vibrator system including a retarded relay with a shunt-connected winding; and

Fig. 3 shows a vibrator circuit embodying the invention and including a difi'erential relay of a retarded type.

Referring now more particularly to Fig. 1, a preferred embodiment of the invention will be described. The circuit essentially comprises a vibratory reed l adapted to cooperate with a pair of relatively fixed contacts II and 2 connected to the ends of primary winding l3 of a step-up transformer l4. The secondary winding i5 of the transformer is grounded at its center tap and is connected to a full-wave rectifier diagrammatically shown at Hi. This rectifier may be a vacuum tube or a separate set of contacts synchronously operable by reed H). An electromagnet I! is connected between reed l0 and one end of primary winding l3 and is adapted to maintain the reed in vibratory motion when a source or low voltage current is connected in conventional manner between reed l0 and the center tap of primary winding |3.

Power is supplied to the vibrator system from a low voltage source through a switch IS, a serially connected choke coil 20, the winding of a retarded relay 2| and a current limiting resistance 22, all in series, said resistance being connected to the center tap of primary winding I3 of transformer i4. Relay 2| is preferably of the ma netically retarded/type in which a delayed closing action is obtained by the provision of a shortcircuit winding or of a copper slug 23 on the iron core into proximity of the winding. In some cases it is desirable to make the degree of the time delay effect adjustable, this being obtainable, for example, by adjustment of the copper slug on the core. An armature 24 and a fixed contact 25 are incorporated into relay 2| and provide a normally open short-circuit path across limiting resistance 22. A condenser 26 is connected between the common point of choke coil 20 and of relay winding 2|, and ground, and a similar condenser 21 is connected between the center tap of the primary winding I3 and ground. The object of these condensers is to provide with choke coil 20 and with the inductance of relay winding 2| a radio frequency "hash" or interference filter to keep such interference as is generated by the vibrator circuit out of the battery circuit. A buffer condenser 28 may be connected across secondary winding I5 of the transformer, for reasons well known by those skilled in the art.

From the foregoing description the operation of the vibrator system illustrated in Fig. 1 will be readily understood. Upon closing switch l9, current will flow from battery l8, through switch l9, choke coil 20, relay winding 2|, current limiting resistance 22, the lower half of primary winding l3, vibrator coil l1 and back to battery I8. Vibrator coil I! will be energized and will deflect reed l0 thereby closing power contact l2 and short-circuiting coil I'I. Coil I1 now being deenergized, reed III will swing back and will close contact I thereby causing current to flow through the other half of the primary winding. It will be noted that current will flow alternately through the two halves of the primary winding and will induce a current of relatively high voltage in the secondary winding l5 which is rectified by rectifler l6. Limiting resistance 22 being in the circuit, the current flowing through the primary winding and interrupted by contacts II and |2 is maintained within preferred values so that excessive arcing of the contact points or discs is positively prevented.

After a predetermined time interval retarded relay 2| will attract its armature 24 which closing contact 25 will short-circuit limiting resistance 22. Thus, practically the full battery voltage becomes effective for actuating the vibrator system, if the slight voltage drop through coil 20 and relay winding 2| is disregarded. The retarding action of the relay is preferably adjusted to about to about 6 of a second which is sumcient to carry out the first 10 to 20. half cycles. After this time the steady-state operating conditions are definitely established. While the amount of time delay is not critical, in some cases it is advantageous to provide for adjustment of the same for example by displacing copper slug 23 with respect to the core. In this embodiment of the invention the retarded relay is serially connected and its winding may be utilized as a choke coil in combination with condensers 2i and 21 and possibly with another choke coil for the purpose of an interference filter.

In the modification shown in Fig. 2, the vibrator system proper is identical with that of Fig. 1 and similar reference characters have been used to denote corresponding parts. Therefore, it will not be necessary to repeat description of this part of. the circuit. A current limiting resistance 32 is interposed in the power supply circuit and may be short-circuited by armature 34 and stationery contact of retarded relay 3|. In this case, however, the winding 0: relay 3| has a relatively high resistance and is voltage operated by having it connected between the s common point Of choke coil20and'of limiting resistance 32 and the other pole of thebattery l8."

In the operation of this circuit currentwillflgw through closed switch l9, choke coil 20, current limiting resistance 32, the lower half of primary winding 13, vibrator coil i1 and back to battery I 8 and during vibrations of the reed Ill current will be caused to flow alternately through the two halves of the primary winding of transformer l4. During the first 10 or 20 half cycles the current to be handled by power contacts II and I2 is restricted to safe values by means of current limiting resistance 32. After a. predetermined lensth of time retarded action relay 3i becomes operative and will short-circuit limiting resistance 32 by armature 34 closing contact 35. Thus, the full battery voltage becomes effective for the vibrator after the initial starting period. y In this embodiment thedelayed action relay is actuated by the battery voltage and consequently is independent of the load. The relay winding cannot be utilized as a choke coil and a separate choke coil 20 is necessary in combination with a condenser 26 forproviding an interference or hash" filter. -While the relay 3| is drawing power from the battery throughout the operation of the vibrator system, this additional load may be maintained quite small by providing the relay with a high resistance winding.

The modified embodiment of the invention illustrated in Fig. 3 may be to some extent considered a combination of the circuits of Figs. 1 and 2. The connections of the vibrator with the step-up transformer are identical with those of the other embodiments and the corresponding parts have been denoted by similar reference characters. Rel'ay 3-9, however, is of the differential type and is provided with a voltage winding 40 and with a current winding 4| so wound as to produce oppositely directed magnetic fields. The series circuit of the system includes battery i3, switch l8, choke coil 20, current coil 41 of relay 39, limiting resistance 42, the lower half of primary winding 13, vibrator coil l1 and back to battery l8. The auxiliary or parallel portion of the circuit includes battery I8, switch i9, choke coil 20, voltage coil 40 of relay 39 and back to battery i8. Armature 44 and contact 45 of relay 38 provide a normally open short-circuiting path for limiting resistance 42.

When initiating operation of the system by closing switch l9, both the voltage coil and the current coil of relay 39 will be energized. During the starting cycles the high surge current flowing through winding 4| of the relay will produce a magnetizing effect equal to or in excess of that produced by voltage winding 40 and will oppose closing of the relay contacts. When the current reaches its normal operating value, the magnetic effect of the voltage coil becomes controlling and closes the relay contacts thereby short-circuiting limiting resistance 42. Thus, in this embodiment the diil'erential effect of a voltage and of a current winding is employed to obtain a time delay or retarded operation of the relay. In many cases, however, it is desirable to supplement this delay action by the provision of a copper slug 43 or of an additional shortcircuited winding on relay 39. In this embodiment one of the relay windings, current coil 4!, may be also utilized as a choke coil in order to provide an interference filter together with condensers 26 and 21 and if necessary with an additional choke coil 20. s

Although the present invention has been described in connection with a few preferred embodiments thereof, variations and modifications may be resorted to by those skilled in the art without departing from the principles of the invention. I consider all of these variations and modifications as within the true spirit and scope of the present invention as disclosed in the foregoing description and defined by the appended claims.

What is claimed is:

1. In combination with a vibrator power supply system having a reed bearing vibratory contacts for making and breaking the continuity of a circuit including a source of current and the primary winding of a transformer, a resistance initially interposed in said circuit to limit the current flowing therein, and a retarded relay under the effect of current flowing in said circuit for short-circuiting said resistance a predetermined time interval after starting the operation of saidreed.

2. In combination with a vibrator power sup- 4 ply system including a transformer with a centertapped primary winding and vibratory contacts for alternately passing current through the two halves of said winding, 9. current limiting resistance interposed in the circuit of said winding symmetrically and equipotentially with respect to the two halves thereof, and a time-delay relay under the eflect ofcurrent supplied to said circuit for short-circuiting said resistance a predetermined time lnterval after starting the operation of said reed.

3. In combination with a vibrator power supply system having a reed bearing vibratory contacts for making and breaking the continuity of a circuit including a source of current and the primary winding of a transformer, a resistance initially interposed in said circuit to limit the current flowing therein, a retarded relay having a coil connected in said circuit for short-circuiting said resistance a predetermined time interval after starting the operation of said reed, and capacitor means for forming aninterference filter with said coil to suppress undesirable oscillatory currents.

4. A vibrator power supply system comprising a source of electric current, a transformer having a center-tapped primary winding and an electromagnetic vibratory interrupter having a vibratory reed connected to one terminal of said source and a pair of stationary contacts alternately engaged by said vibratory contact during vibration thereof and respectively connected to the ends of said primary winding, the center of said winding being connected to the other terminal of said source. a switch in series with said source, a limiting resistance in series with said source, a retarded relay having a coil in series with said source, and contact means operable by said relay adapted to short-circuit said resistance a predetermined time interval after said coil has been energized.

5. In combination with a vibrator power supply system having a reed bearing vibratory contacts for controlling then current flow through a circuit including a source of current and the primary winding of a transformer, a main switch and a current limiting resistance in series with said source of current, a retarded relay having a coil connected across said source after said switch adapted to be energized from the source at a voltage substantially independent from the load when said switch is closed, and contact means operable by said coil to short-circuit said resistance a predetermined time interval after said switch is closed.

6. In combination with a vibrator power supply system having a reed bearing vibratory contacts for controlling the current flow through a circuit including a source of current and the primary winding of a transformer, a main switch and a current limiting resistance in series with said source of current, a differential relay having a voltage coll connected across said source after said switch and a current coil connected in series with said source, and contact means operable by the joint effect of said coils to short-circuit said resistance, the relative magnetizing effect of said coils being so determined that during the initial starting surge the current coil is controlling to maintain said contact means inoperative and that during normal steady operation the voltage coil is controlling to render said contact means operative.

7. In combination with a vibrator power supply having a reed bearing vibratory contacts for controlling the current flow through a circuit including a source of current and the primary winding of a transformer, a main switch and a current limiting resistance in series with said source of current, a differential relay having a voltage coil connected across said source after said switch and a current coil connected in series with said source, contact means operable by the joint client of said coils to short-circuit said resistance, the relative magnetizing efiect of said coils being so determined that during the initial starting surge the current coil is controlling to maintain said contacts means inoperative and that during normal steady operation the voltage coil is controlling to render said contact means operative, and means operatively associated with said relay to delay actuation of said contact means after said coils are energized.

THEODORE N. ROSSER.

REFERENCES CITED Thefollowing references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,921,461 Garstang Aug. 8, 1933 2,240,123 Shoup et a1 Apr. 29, 1941 2,362,028 Rosser et al Nov. 7, 1944 

